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Agonist vs. antagonist. In pharmacology the term agonist-antagonist or mixed agonist/antagonist is used to refer to a drug which under some conditions behaves as an agonist (a substance that fully activates the receptor that it binds to) while under other conditions, behaves as an antagonist (a substance that binds to a receptor but does not activate and can block the activity of other agonists).
Whereas D 2 receptor agonists suppress prolactin secretion, dopamine D 2 receptor antagonists like domperidone and metoclopramide have the opposite effect, strongly inducing the pituitary secretion of prolactin, and are sometimes used as prolactin releasers, for instance to correct hypoprolactinemia (low prolactin levels) in the treatment of lactation failure. [2]
A co-agonist works with other co-agonists to produce the desired effect together. NMDA receptor activation requires the binding of both glutamate, glycine and D-serine co-agonists. Calcium can also act as a co-agonist at the IP3 receptor. A selective agonist is selective for a specific type of receptor. E.g.
An adrenergic agonist is a drug that stimulates a response from the adrenergic receptors. The five main categories of adrenergic receptors are: α 1 , α 2 , β 1 , β 2 , and β 3 , although there are more subtypes, and agonists vary in specificity between these receptors, and may be classified respectively.
An example is found in medications used to treat opioid addiction, with methadone, buprenorphine, naloxone, and naltrexone all in separate categories or in more than one simultaneously. In addition, depending on the cell type, the specific effect, whether agonist, antagonist, inverse agonist, etc., could have a unique specific effect.
Beta adrenergic agonists or beta agonists are medications that relax muscles of the airways, causing widening of the airways and resulting in easier breathing. [1] They are a class of sympathomimetic agents, each acting upon the beta adrenoceptors . [ 2 ]
α 2 agonist: inhibits adenylyl cyclase activity, reduces brainstem vasomotor center-mediated CNS activation; used as antihypertensive, sedative & treatment of opiate dependence and alcohol withdrawal symptoms). Selected examples are: Brimonidine; Clonidine (mixed alpha2-adrenergic and imidazoline-I1 receptor agonist) Dexmedetomidine; Fadolmidine
β 1-Adrenergic receptor agonists, also known as beta-1 agonists, are a class of drugs that bind selectively to the β 1-adrenergic receptor. As a result, they act more selectively upon the heart . β-Adrenoceptors typically bind to norepinephrine release by sympathetic adrenergic nerves and to circulating epinephrine .